1. Field of the Invention
This invention relates to the field of plasma display panels, in particular, to a method of forming ribs by transfer-printing a glass paste filled in a recess of a mold which has a configuration suitable for transfer-printing, and to a rear plate unit of a plasma display panel formed by the method.
2. Description of the Related Art
There are some methods of forming ribs of the plasma display panel, such as a screen printing method, a sandblasting method and so on.
In the screen printing method, a material for ribs (a glass paste) is made up by mixing of glass having a low melting point, a metal oxide such as alumina, vehicles and so on. The material for ribs is transfer-printed in a predetermined pattern on a glass substrate by a screen printing and then is dried up. The steps of printing and drying are repeated about 8 to 15 times so that the pattern for ribs are piled up to about 150xcexcm. The piled pattern is then heated to form the intended ribs.
In the sandblasting method, the material for ribs described above is applied wholly on the glass substrate in such a manner that the thickness of the material for ribs is about 200xcexcm. Then a dry-film-photoresist is attached on the surface of the material for ribs and is formed into a resist pattern by exposure to light. Then, the portions of the material for ribs not covered with the resist pattern are removed by sandblasting. Then, the resist pattern is melt and removed with caustic soda. The portions of the material for ribs covered with the resist pattern are then heated to form the intended ribs.
The screen printing method costs less because it can use the screen printing press. The screen printing method has also an advantage of small loss of the material because the material is printed only in a pattern corresponding to the intended ribs.
However, in conventional screen printing method, the heights of the ribs tend to be uneven, and some ribs may collapse as the printing is repeated. In addition, the conventional screen printing method is difficult to cope with fine pitches because there is a limitation to printing precision.
On the other hand, the sandblasting method has an advantage in that it can form higher precision patterns than the conventional screen printing method.
However, the sandblasting method does not make efficient use of the material for ribs, so that it can yield much waste.
A method of forming ribs by transfer-printing a glass paste filled in a recess of a mold on a glass paste has been suggested to solve the problems. For example, Japanese Patent Laid-Open 8-273537 describes a method comprising: providing a mold-sheet having a recess by using an intaglio, filling the recess of the mold-sheet with a glass paste, sticking the mold-sheet to a glass substrate, and removing the mold-sheet from the glass substrate to transfer-print the glass paste on the surface of the glass substrate. According to the method, the ribs are formed with an increased efficiency in using the material, without producing a waste, at high speed and with high precision. The above method requires that the glass paste come off substantially completely from within the recess of the mold-sheet to transfer-print the glass paste on the glass substrate in a predetermined shape.
Therefore, the object of this invention is to provide a method of forming ribs of a plasma display panel wherein a glass paste comes off substantially completely from within a recess as the glass paste is being transfer-printed onto a glass substrate, and a rear plate unit of a plasma display panel whose ribs are formed by the method.
To achieve the above object, this invention is characterized by the following features. That is:
This invention is a method of forming ribs of a plasma display panel by transfer-printing a glass paste on a glass substrate, comprising: providing a mold recess having a configuration corresponding to ribs arranged in parallel with each other and a joining element joining the ribs; filling the recess with the glass paste; and starting transfer-printing the glass paste on the glass substrate from a portion of the glass paste corresponding to the joining element filled in the recess.
According to the invention, in the mold recess having the configuration corresponding to the ribs arranged in parallel with each other and the joining element joining the ribs, the transfer-printing operation of the glass paste onto the glass substrate is started from the portion of the glass paste filled in the recesses, corresponding to the joining element. That is, the joining element becomes a starting point for the transfer-printing. The ribs joined by the joining element are transfer-printed following the joining element because the forces for transfer-printing the ribs are generated by the transfer-printing of the joining element. Thus the method of forming ribs of a plasma display panel may achieve that the glass paste comes off substantially completely from within the recess as the glass paste is being transfer-printed onto the glass substrate.
The recess is preferably formed in a mold-sheet in such a manner that the recess has a configuration having an opposite concavo-convex relation with the ribs and the joining element.
The recess may be formed in a flexible roller-intaglio in such a manner that the recess has a configuration having an opposite concavo-convex relation with the ribs and the joining element.
The method of forming ribs of a plasma display panel preferably comprises: heating the transfer-printed glass paste for hardening.
This invention is also a rear plate unit of a plasma display panel comprising: a glass substrate; ribs arranged in parallel with each other on the substrate; and a joining element arranged on the substrate and joining the ribs.
According to the invention, as the joining element joins the ribs arranged in parallel with each other, the rear plate unit of a plasma display panel may be easily formed by the method of forming the ribs by transfer-printing the glass paste filled in the recess.
The joining element is preferably formed in a bank shape and joins end portions of the ribs. In this case, as the end portions of the ribs are joined by the joining element of the bank shape, the forming of the joining element has little restriction but much advantage. In addition, the joining element has a height which is preferably lower than heights of the ribs and is gradually reduced in a direction away from the end portions of the ribs.
The joining element may be formed in a sheet shape and joins lower portions of the ribs. In this case, as the lower portions of the ribs are joined by the joining element of the sheet-shaped, the joining element serves as a starting point for the transfer-printing and operates to generate the forces for transfer-printing the ribs following the joining element. In this case, the ribs have heights which are preferably gradually reduced toward the end portions of the ribs. In addition, in this case, the joining element is preferably provided on an address electrode to form a dielectric layer. Then, as the dielectric layer is formed on the address electrode by the sheet-shaped joining element, the step of only forming of the dielectric layer can be omitted.